The present invention relates to a copper radiator for motor cars wherein corrosion resistance of the fins is improved, and lightening in weight and high performance of the radiator is effected, and to a method for its manufacture.
The purpose of a radiator in motor cars is to cool the heat-exchanging medium by a stream of air passing therethrough. It is constructed generally as shown in FIG. 1, wherein fins (2) greatly expanding the cooling aid radiation area are provided between many flat tubes (1), at least one surface of the tubes or fins is covered with brazing material, and these tubes and fins are temporarily assembled. Then, this temporary assemblage is dipped into a flux solution or the flux solution is coated onto the surface thereof and thereafter the assemblage is heated in an air atmosphere. Then the brazing material is allowed to melt by this treatment and the molten brazing material is spread sufficiently all over the contact places of the tubes with the fins, it is allowed to solidify and bonding of tubes to the fins is effected to form core (3).
The flux adhered on the surface of the temporary assemblage functions also to remove the oxidized film produced on the surface thereof and to improve the wettability of the brazing material when the temporary assemblage is heated in the atmospheric air.
Further, seat plates (4) and (4') are fitted to one end or both ends of said core (3) (fitting to both ends is shown in the Figure) by soldering and tanks (5) and (5') are connected to these seat plates. In general, for the tubes, copper alloys, such as brass, etc., are used. For the fins, thin plates made from high heat-conductive copper or copper alloys such as Cu-Sn, Cu-Cd, Cu-Zr, Cu-Ag, etc., subjected to a corrugation or louver treatment are used, and, for the seat plates, brass plates are used. Also, for the tanks, those made from brass have been used and connected by soldering, but resinous tanks have recently been used for lightening in weight and being connected by mechanical crimping.
Recently, in view of the demand for lightening in weight and high performance of the total car, lightening and high performance of the radiator for motor cars also have been investigated. As a result, thinning and the high densification of fins are regarded as effective means, and, for the fins, a plurality of thin plates (thickness: 0.02-0.05 mm) made from high heat-conductive copper alloys aforementioned is used. Although copper and copper alloys are excellent in corrosion resistance when originally installed, with the recent advent of the use of much chloride as a snow-melting agent, corrosion due to snow damage has become a serious problem with the radiator. Thus, the snow-melting agent scattered in large quantities sticks to the radiator and corrodes the fins at an extraordinarily high rates so as to decrease the effective radiation area resulting in a drastic lowering in the performance of the radiator in a short period of time.
Moreover, by the method as described above, since the temporary assemblage is heated in atmospheric air, relatively large amounts of oxidized film are produced on the surface of the temporary assemblage in a short period of time. Thus, there arises a problem that, if the oxidized film is produced in large amounts, an excess of flux becomes necessary and, the greater the amount of flux, the more of the flux decomposes thermally, inducing malodor.
Further when the molten brazing material solidifies and the bonding of tubes with fins is completed, the assemblage should be washed to wash out the flux remaining behind on the surface thereof. However, as described above, if an excess amount of flux is used, the heavy metals in the flux flow out into the wash effluent at an increasing rate causing effluent contamination.
In order to prevent this, various methods have been investigated, but all of them are insufficient. For example, coated film with a thickness of more than 0.01 mm becomes necessary. Prevention by coating, however, practically is inferior because of an increase in weight and a rise in cost. Moreover, if fins are formed with Cu-10% Ni alloy known as a corrosionresistant copper alloy to make fins more corrosionresistant, the radiation property significantly decreases with a plate of same thickness. Thus, when comparing by the electroconductivity proportional to the thermal conductivity, the relation being known as the Wiedemann-Franz's law, Cu-10% Ni alloy shows less than 10% IACS to 90 to 80% IACS with usual fin materials.
The invention provides methods of economically manufacturing a copper radiator for motor cars of high performance and withstanding corrosion due to snow damage, and at the same time lightening the car and no malodor and effluent contamination being present.